1. Field of the Invention
The present invention relates to throttle devices for internal combustion engines, and in particular to throttle devices having electrically-driven actuators that are actuated to open and close throttle valves for controlling the flow of intake air to be supplied to internal combustion engines.
2. Description of the Related Art
Throttle devices are known that include electrically-driven actuators, such as DC motors and stepping motors, which are actuated to open and close throttle valves. This type of throttle device is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2000-110589. According to this publication, a throttle valve is held at an opener opening angle that is larger than an opening angle at a fully closed position of the throttle valve when no power is supplied to an electrically-driven actuator. The term “opener opening angle” is used to mean an open angle set by an opener.
The throttle device of the above publication will be described with reference to FIGS. 15 and 16. As shown in FIG. 15, a throttle gear 143 is mounted to a throttle shaft 103 of a throttle valve 10 that can be rotated to open and close an intake air channel 101 defined within a throttle body 100. An engaging lever 106 is loosely fitted about the throttle shaft 103, so that the engaging lever 106 can rotate about the throttle shaft 103. The throttle gear 143 is a final stage gear of a gear mechanism for transmitting rotation of a motor 105 to the throttle shaft 103. A default spring 108 is a torsion coil spring and is interleaved between the throttle gear 143 and the engaging lever 106. The default spring 108 serves to resiliently keep engagement between an engaging edge 143a of the throttle gear 143 and an arm portion 162 of the engaging lever 106. A return spring 107 is a torsion coil spring and is interleaved between the throttle body 100 and the engaging lever 106. The return spring 107 serves to bias the engaging lever 106 in a closing direction. An engaging portion 161 of the engaging lever 106 can contact a stopper 111 that is mounted to the throttle body 100 for setting a default open angle, so that the engaging lever 106 can be prevented from rotating to result an open angle that is smaller than the opener open angle. Therefore, when no power is supplied to the motor 105, the engaging lever 106 contacts the stopper 111 by the biasing force of the return spring 107, while the throttle gear 153 and the engaging lever 106 engage with each other by the biasing force of the default spring 108. As a result, the throttle valve 102 can be held at the opener opening angle. The engaging lever 106, the return spring 107, the default spring 108, the stopper 111 and the throttle gear 143 constitute a default open angle setting mechanism.
In the above throttle device, in order to mount the default spring 108 to the engaging lever 106, a hook 108b is formed on the default spring 108 by bending a terminal end of the default spring 108 outwardly in a turn back manner. The hook 108b engages a spring engaging portion 164 of the engaging lever 106. The spring engaging portion 164 has a configuration like a pin. This mounting structure has a problem that the operation for engaging the hook 108b with the spring engaging portion 164 cannot be easily performed. In addition, a possibility may exist that the hook 108b is accidentally removed from the spring engaging portion 164.
Therefore, there has been a need for throttle devices that can facilitate the mounting operation of a torsion coil spring to a spring mount and can prevent or inhibit the torsion spring from being removed from the spring mount.